Microfluidic systems are used especially in analytical systems for body fluids for example in blood sugar measuring instruments which diabetics can use themselves to monitor their blood sugar level. The system comprises a lancing member which is connected to the microchannel for the capillary transport of a body fluid. The fluid is transported by the microchannel to a collecting area in order to detect the respective measured quantity, for example the blood sugar content, separately from the lancing site. Such systems are disclosed for example in WO2006/021361 and EP 1671585, both of which are hereby incorporated by reference in their entirety, to the contents of which explicit reference is made especially with regard to the manufacture of such microstructures.
The microchannel and optionally the lancing member are manufactured from a biocompatible material i.e. a material that is inert especially towards the body fluid, which has to be capable of being mechanically stressed as well as easy to clean and sterilize. Surgical steel, such as 316L steel, for example, is particularly suitable for this but is not sufficiently hydrophilic to allow a capillary transport of aqueous body fluids through the microchannel. For this reason durable and stable hydrophilic surface coatings are sought which are also biocompatible. In addition the surface coating must allow the microchannel to fill within a very short time, preferably less than two seconds so that the body fluid can be collected rapidly. This is especially important for collecting blood for determining the blood sugar content because coagulation reactions would not yet be expected within such a short period such that the user very rapidly obtains a measuring result. Moreover, the surface coating must be compatible with at least one sterilization method, such as sterilization by means of electron rays (β-radiation), for example.
Finally an adequate long-term stability of the surface coating is desirable. This poses a problem because hydrophilic coatings usually have high-energy surfaces. This is generally thermodynamically unfavorable because the surface attempts to reduce its high energy by reducing the hydrophilicity.